The earth has gotten greener…




  • NASA satellites observed greening during the 21st century
    • populous and developing countries
    • regions far removed from human reach


  • Svalbard, in the high-arctic, 30% ↑ greenness
    • concurrent with ↑ in summer temperature from 2.9 to 4.7C


  • What is the role of plants in global change?
    • question is a matter of scale

Leaf area index: What it means to be greener


Why are plants producing more leaf area?






  • Humans dump ~40 billion tons of CO2 into atmosphere
    • EACH YEAR


  • Atmospheric CO2 is a greenhouse gas
    • ↑ CO2 = ↑ trapped heat = ↑ surface temperatures


  • Plants fix CO2 from the atmosphere via Rubisco

Greenhouse gases make the earth warm


A carbon imbalance exists between surfaces and air


Plants represent a large carbon sink


The role of vegetation change





  • Ability to immediately fix carbon from atmosphere
    • photosynthesis - respiration
    • keeping pace with human emissions?


  • Sequestrating carbon in wood
    • prevents fast cycling of carbon


  • Transpiration adds H2O into atmosphere
    • power greenhouse gas

Plant carbon uptake is multi-layered


Vegetation change is not new!


Global plant C sink: Photosynthesis


Just plant tons of trees, problem solved…





  • Are all trees carbon vacuums?
    • fast growing trees don’t live as long
    • fast growing trees drain more water
    • fast growing trees create less dense wood


  • Farmland to forests: can we eat?


  • Are all forests equal?
    • forest plantation = rain forest?

How sustainable is the CO2 fertilization effect


Global plant C sink: Nutrient limitation


Global plant C sink: Climate warming


Global plant C sink: Climate warming




  • Plants like higher temperatures to a degree
    • faster rate of photosynthesis (limited)
    • most plants not operating at Topt


  • Rubisco cheats more at high temperatures


  • Dependent on stomatal behavior


  • Warming may also mean ↓ precipitation

Global plant C sink: Respiration


Climate change is altering precipation regimes


Key questions: How plastic are plants?



  • Phenotypic plasticity: allows individuals to respond to change within their lifetime
    • acclimation (lifetime) vs adaptation (generations)


  • Can plants change physiology to match new conditions?
    • can optimums be adjusted?


  • Why might northern species struggle in warmer temperatures?


  • Why might plants struggle in new precipitation regime

Climate changes are just part of global change



  • Lots of other stresses on plant communities
    • impact sustainability of greening earth


  • Habit degradation from human activities


  • Total habitat loss
    • agricultural conversion
    • urban growth


  • Higher rates of exotic species invasions

Is the earth still getting greener?



  • Greening since 1980’s reduced warming ~0.2C


  • New science suggests browning trend
    • greening trend stalling or reversing


  • Related to less moisture in the air
    • higher VPD from climate warming


  • Why would drier air impact plant growth negatively…


  • Plant carbon sink does not fix global carbon imbalance